Japanese Cannabis Users Rarely Progressed to Other Drugs, Challenging the Gateway Hypothesis

Tobacco and alcohol were the most common initial substances, with cannabis typically third. The odds of progressing from cannabis to other substances were low: alcohol 1.25, tobacco 0.77, methamphetamine 0.08, other illicit drugs 0.78. Nearly half of those who reported cannabis as their third drug did not use other substances afterward.

Anonymous online survey of 3,900 individuals reporting lifetime cannabis use in Japan, recruited via social media in January 2021. Substance use progression was visualized using a Sankey diagram. Odds ratios calculated for likelihood of using other substances following cannabis use.

Japan maintains some of the strictest cannabis laws globally, making this a unique context for testing the gateway hypothesis. Even in a prohibitionist setting, cannabis rarely led to harder drug use, suggesting the "gateway" pattern is not an inherent property of cannabis itself.

The gateway drug hypothesis has been a cornerstone of drug prohibition policy worldwide. This study from Japan, where cannabis use carries severe legal penalties, finds little support for the theory even in a context where cannabis users might be more risk-tolerant than in lenient jurisdictions.

Online convenience sample may over-represent younger, tech-savvy users. Self-reported data may be affected by recall bias. Japan's strict drug enforcement may suppress progression to other drugs through deterrence rather than disproving gateway mechanisms. Social media recruitment introduces selection bias.